In general, wind energy installations include a tower with a nacelle mounted on the tower that can be rotated on an approximately vertical rotational axis. A rotor is attached to the nacelle to be able to rotate on a usually horizontal rotational axis.
The rotor of conventional wind energy installations includes a hub and usually two, three, or four rotor blades. The rotor blades fan out from the hub radially about the rotor axis. In order to adapt the characteristics of the rotor to prevailing wind conditions, the rotor blades are usually rotatable with respect to rotational axes aligned radially to the rotor axis. For this purpose, hydraulic cylinders and/or servo-motors with the necessary gears are often built into the hub. These servo-motors as well as the gears and generators downstream of the rotor, which are also usually mounted on the nacelle, represent a potential source of malfunction during operation of the wind energy installation. Repair and maintenance personnel must be able to access the parts of the installation that are mounted in or near the rotor hub. In order to avoid damage to the wind energy installation, the rotor must be stopped and locked during maintenance and repair.
According to the applicable guidelines for the certification of wind energy plants, provision must be made for the positive locking of the rotor. For this purpose, pins or locking devices are usually used that fit into disks coaxially attached to the rotor in a non-rotatable manner. Conventional locking pins are fixed with respect to rotation on the rotor axis and are braced in the required rotational direction on the frame structure of the wind power installation, in this way making possible a positive locking with respect to rotation on the rotor axis, in concert with the disks that are non-rotatably attached to the rotor. To reach the locking position, the pins of conventional locking devices are adjusted manually or hydraulically along the axis of the pins which runs approximately parallel to the rotor axis between a release position and a locking position, in which the pins fit into a recess in the disk. To obtain the required locked position, an aerodynamic and/or mechanical brake is applied to the rotors of the wind power installation until they come to a standstill. Then the locking pin is moved to the locking position in which it fits into the recess in the disk. It has become evident that the conventional way of locking cannot be accomplished without the use of service personnel on the nacelle. This not only represents higher costs but also increases the risk for maintenance personnel, who must be ferried to the top of the nacelle, which in the case of modern wind energy installations is usually mounted at a height of 100 m or more, while the rotor is in motion.
When wind energy installations are deployed off-shore, their accessibility may be restricted by a variety of factors including high waves or ice. At times the wind energy installations are accessed by helicopter and service personnel are ferried to the top of the nacelle (turbine house). These maneuvers are very risky because wind conditions vary continuously as the rotor continues to rotate slowly.